Hard rock grinding mills used in mineral processing utilize sacrificial segmented liners bolted to the internal casing of the mills which are regularly replaced during routine maintenance. Typically such mills may range in size from three meter to eleven meter diameter and are lined with replaceable heavy steel segments attached internally to the mill casing by through bolting. As the sacrificial liners wear, it becomes necessary to remove the bolts that held the sacrificial liner in place and reline the mill. In the last twenty-five years, considerable advances have been made to mechanize the mill relining process, including the use of liner bolt removal tools, an example of which is shown in WO 1997/026116 (Russell Mineral Equipment Pty Ltd) and mill relining machines an example of which is shown in Australian Patent No. 2005239667 (Russell Mineral Equipment Pty Ltd).
It has been identified that mill liner life dictates the ‘when’ of mineral concentrator maintenance shutdowns. Furthermore, the exchange of mill liners dictates the duration of each shutdown; the ‘how long’. In combination (the ‘when’ and the ‘how long’) dictate annual maintenance shutdown lost time and therefore the availability and the possible utilisation of the mineral concentrator plant.
Since all mineral ore of value must pass through the grinding mill, liner life and liner exchange rate can define the productive limits of the entire mine site.
The duration of a mill reline is the sum of thousands of discrete and interdependent activities. The choreographing of these activities occurs in an environment that is often noisy, full of other unrelated work and where the visibility of, and communication with, dependent activities is often obscured by the mill itself. Because of the complexity of the interplay between tasks and the difficulty of quantifying them the estimation of reline times has, in most cases, been reduced to assigning an average time per piece, based on historical data, to each type of liner and multiplying this by the number of pieces to be changed.
There are four major contributors to controlling the timing of mill relining shutdowns and the speed of liner exchange, these being the liners themselves (their size and quantity); the reline planning process and relining crew proficiency; relining equipment; and plant design surrounding the grinding mills.
The state of the art for estimating reline times is based on somebody familiar with mill relining estimating the time per type of liner and multiplying by the number of liners to be changed. Most if not all methods are spreadsheet based and are incapable of predicting the effects of small changes to the process. The cost for a mill to be shut down for relining is very high, and often is of the magnitude of hundreds of thousands of dollars per hour.
To date, the methods to estimate reline times have been quite crude, and do not provide mill owners, plant and machine designers and reline planners with the ability to maximize plant efficiency.
The ability of mill owners, plant and machine designers and reline planners to estimate re-line times is usually based on their own experience. The impediments they face to maximize reline times are the large number of variables, the low frequency of relines and the economic risk associated with some changes. Also their ability to maximize the efficiency of their plants suffers from the lack of opportunity to effectively benchmark current performance against best practice.
The present invention seeks to provide a method and system for simulating a mill reline that can ameliorate at least some of the disadvantages of the prior art.